Sets the request id in order to link together events into a single session (the
span of events between the time that the server initiates a single U2F request
to the client and receives a reply) on a single device.

Sets the request id in order to link together events into a single session (the span
of events between the time that the server initiates a single U2F request to the client
and receives a reply) on a single device. This field is optional.